Electric heaters



March 9, 1965 J. D. WILKINS ELECTRIC HEATERS 2 Sheets-Sheet 1 Original Filed Sept. 4, 1959 FIG. 2

INVENTOR.

JOHN D. WI LKINS A TTORNE Y March 9, 1965 J. D. WILKINS 3,173,124

ELECTRIC HEATERS Original Filed Sept. 4, 1959 2 Sheets-Sheet 2 INVENTOR. JOHN D. WILKINS ATTORNEY United States Patent Office 3,l?3,l24 Patented Mar. 9, 1965 3,173,124 ELECTRIC HEATERS John D. Wilkins, St. Louis, Mo., assignor to Olin Mathieson Chemical Corporation, East Alton, Ill., a corporation of Virginia Original application Sept. 4, 1959, Bar. No. 838,274, new Patent No. 3,137,924, dated June 23, 1964. Divided and this application July NI, 1962, Ser. No. 220,111

Claims. (Cl. 338-417) This invention is directed to electric heaters and more particularly to sheathed resistance heaters and to a method for making the same.

This application is a division of co-pending application Serial No. 838,274, filed September 4, 1959, now US Patent 3,137,924, issued June 23, 1964.

Heretofore the manufacture of sheathed electric resistance heaters comprised the usual steps of positioning an electrical resistance element coaxially within a straight deformable tube of generally rounded cross-section while still straight, the tube was then filled with a heat-conducting electrical-insulating material such as magnesium oxide. Thereafter, in the manufacture of electric range hot plates and the like, the tube was then bent into a Hat spiral of any appropraite radius, and then compressed radially to obtain the desired cross-sectional configuration, usually in a flat-top shape. During deformation of the tube into a fiat spiral by bending operations, the insulating filler material is subjected to stresses which often fragments it and causes voids which detract from reliability and etficiency of the unit. Also, during the alteration of the cross-section of the sheet by bending and pressing operations to obtain a desired shape, stresses are transmitted to the electrical element sheathed therein and cause the element to fracture, thus opening the circuit and rendering the heating unit useless. For more tortuous and extensive heaters than range hot plates, these disadvantages are aggravated.

Where a heating element was desired to be tortuously or convolutely distributed within a common structure, the aforesaid sheathed heating unit has heretofore been shaped into the desired configuration of the desired structure, and molten metal was poured into the mold so as to be cast about the shaped, sheathed heater unit. Various inherent disadvantages are present in the last said process. A particular one involves the introduction of additional barrier to heat transfer in the heat element in the form of the inner base formed between the metal of the structure and the metal of the sheet. Additional disadvantages that may be mentioned are those inherently present and referred to above resulting from deformation of the sheathed unit into desired spatial configuration about which the structure is molded.

Heretofore no process has been known or advanced for sheathing an electrical resistance element within a tubular structure extending in a tortuous curvilinear or multi-directional pattern.

Accordingly, it is an object of this invention to eliminate disadvantages of the prior art relating to the manufacture of such heaters.

Another object of this invention is to provide novel electrical heaters and a novel process for the manufacture thereof.

Another object of this invention is to provide a novel method for sheathing an electric resistance element within a tortuously extending tubular cavity.

A further object of this invention is to provide a novel method for sheathing an electrical resistance heating unit without subsequently disturbing insulating and conducting materials therein.

A still further object of this invention is to provide a novel solid electric heater having internally therein a tortuously extending cavity with an electrical resistance element sheathed therein.

FIGURE 1 is a plan view partly in section illustrating one embodiment of this invention for sheathing an electrical resistance element within tortuous passages contained in a solid sheet structure;

FIGURE 2 is a perspective view illustrating a portion of novel means employed for sheathing an electrical resistance element according to the embodiment of FIGURE 1;

FIGURE 3 is a sectional view taken along lines III-III of the embodiment of FIGURE 1;

FIGURE 4 is a partially sectional view illustrating one suitable type of an electrical resistance element to be sheathed in the embodiment of FIGURE 1;

FIGURE 5 is a sectional view of another electrical resistance element that can be sheathed in the embodiment of FIGURE 1;

FIGURE 6 is a plan view partially in section illustrating another embodiment of this invention;

FIGURE 7 is a sectional view taken along lines VIIVII of the embodiment of FIGURE 6;

FIGURE 8 is a perspective view of a portion of another novel means for sheathing an electrical resistance element in the embodiment of FIGURE 6;

FIGURE 9 is a cross-sectional view taken along lines IX-IX of FIGURE 8; and

FIGURE 10 is a sectional view illustrating an electrical resistance element sheathed in the embodiment of FIG- URE 6.

In accordance with this invention the above objects and other objects can be obtained by fluid driving the electric conductor and insulation together as a unit into a platelike sheath. This is done, for example by attaching an electrical resistance element to a travelling leader plug which is propelled through tortuously a preformed pattern of extending inchoate hollows of uniform width which are contained within a solid structure and which at some stage fit the plug. Generally speaking, this is accomplished by mounting a plurality of insulating members at suitably spaced points on the resistance element, one end of which is attached to the aforesaid leader plug. The leader plug is then inserted into one end of the tortuously extending hollow to be filled and propelled therethrough by some appropriate means. In one embodiment fluid injection and inflation are contemplated. The hollow containing the heater structure may be of any desired final configuration, such as cubic, spheroidal and the like. The invention, however, Will be described with reference to the patterned panels obtained by the well known roll forged process disclosed in the patent to Grenell, US. No. 2,690,002 granted on September 28, 1954.

In the process of the aforesaid patent, a pattern of Weld-inhibiting material is interposed between superposed component sheets of metal and the sheets secured together to prevent relative movement therebetween. The secured superposed sheets are then welded together, as by hot-rolling, in the adjacent areas thereof which are not separated by the weld-inhibiting material. The particular pattern of weld-inhibiting material may be applied in any desired configuration to define any desired complex system of passageways depending on the particular application desired for the welded unit. Upon welding of the uusepearated portions of the welded unit, the applied pattern of weld-inhibiting material results in an unjoined portion or lamin-ations extending between the sheets and between the unjoined portions thereof. These unjoined portions are then permanently distended by ex" pansion thereof with fluid pressure and the like to form the desired system of tubular passageways. The welded sheets may be utilized in various ways, such as baseboard heaters or refrigerator evaporator plates and the like.

Also, these welded sheets may be, either prior to or subsequent to expansion of the laminations therein, further fabricated into any structural configuration desired, as for example bending of the refrigerator evaporator plate to define a freezer compartment within a refrigerator. For the purpose of this invention, the panel before injection of the heater may be fully inflated, only partially inflated, or not inflated at all. Both of the latter are preferred, especially the last which enables simultaneous inflation and injection.

More specifically, with reference to FIGURE 1, a pressure-welded panel, such as obtained by the process of the aforesaid patent, is generally indicated as 1. This panel was formed from two component sheets 2 and 3 between which was interposed a pattern of weld-inhibiting material 4 in a pattern defining a convolutely wound system of unjoined portions or laminations. The electrical resistance element 5, such as the nickel-chrome alloy types, to be sheathed within panel 1 has mounted thereon a plurality of spacer members 6. ments are flexible and of sufficient strength toresist breakage when subjected to the tensile forces required for sheathing it within panel 1. The element may comprise a wire 7 or a wire coiled into helical form 8, or if desired, may be helically coiled about an electrically insulating thread, such as glass, for support thereon.

The spacing members 6 are bead-like members of a material such as magnesium oxide that is heat conducting but electric-insulating, they may be of any suitable configuration desired, but preferably the spacers are spheroidal, such as round beads, or discus-shaped, all strung on the conductor. These spacer members are mounted at spaced points on the resistance element in a suitable or convenient manner. However, it is not necessary that the members themselves may abut each other as illustrated in FIGURE 5. However, if the members are spaced from each other, it is only necesary that they be such as to prevent sagging of the resistance element, in its extended form within the sheet.

The members may be mounted on the resistance element by embedding the element during the molding of the members as indicated at 9 in FEGURE 4 or the resistance element may be threaded through suitable apertures in the members as in 1d at FIGURE. 5. These members function as supporting means for the resistance element within the sheet and also to space the resistance element from the inner wall of the sheet to prevent shorting therewith.

The size of the spacing members as will be understood is dependent on the cross-section of the sheet, and the spacing member may have a maximum cross-sectional dimension equal to corresponding dimensions of the internal cross-section of the subsequently distended tubular hollows in the sheet. However, the spacing member is preferably smaller than the internal cross-section of the distended lamination for purposes hereafter discussed.

The electrical resistance wire for convenience may be mounted on a spool 11 mounted within a suitable container 12 having a pressurizing conduit l3 and an outlet port 14 from which extends any suitable nozzle 15, flexible or rigid, the end of which is inserted into the unjoined portion 4 at 16. In order to insert nozzle 15 into the l-aminations, the laminations may be pried apart and distended at I16 to provide a suitable opening for reception of the nozzle end.

One end of the resistance element 15 is suitably attached to stem 10 by threading the end of the element through an opening 17 and securing it therein by looping the thread upon itself as at 18. Stem 10 is integral with the flared end 19 of a pilot or leader plug 29. This plug flares outwardly and rearwardly from a common point 21 to a terminal portion 22 having the cross-section necessary to provide the necessary distention of lamination 8 when the plug is propelled therethrough. As in the instant embodiment, the cross-section of the terminal por- Generally, these eled tion 22 of plug 20 will generally correspond to the cross sectional configuration 23 desired in distended unjoined portion 4.

In the sheathing operation of this invention, plug 21 may be positioned at any portion within nozzle 15, the terminal end of which is inserted into the unjoined portion 4 at the opening provided at 16. After insertion of nozzle 15 into the unjoined portion 4, appropriate fluid pressure is then injected into container 12 at a suflicient level to propel or drive the leader plug 2t? through the unjoined portion 4 until the plug emerges from the sheet at the unjoined portions terminal end 24. Upon travel of the leader plug through the unjoined portion 4, each portion thereat is distended to assume the cross-section indicated by 26. Since metal inherently has spring-bacl so that it will recover after removal of stresses applied against it, the terminal portion 22 of leader plug 20 has preferably larger cross-sectional dimensions than corresponding dimensions of spacer members 6'. The difference between corresponding cross-sectional dimensions of the spacer member and the terminal portion of the plug is generally equal to the amount of recovery in the metal at maximum corresponding portions of leader plug 20. If desired, although not required the distended unjoined portions t may be additionally shaped by positioning the panel between spaced apart platens at a sulficient distance to constrain the flat top portion 27 of tubular cross-section as against the fiat top portion 28 of the terminal portion 22 provided in leader plug 20.

As will be understood, any fluid, as air, water, steam, and the like, may be employed provided it can be conveniently removed or driven oil, as for example by evaporation, without leaving any electrically conducting residue to short out the resistance element. Preferably the propelling fluid is a slurry of material such as magnesium oxide which is heat-conducting and electrically insulating. This slurry may be contained within container 12 and the pressurizing fluid injected into conduit 13 on the slurry 25. In order to obtain the objectives of this invention, it is only necessary that the consistency of the slurry have sufficient viscosity to propel leader plug 20 through the unjoined portion 4 within the panel 1. After the resistance element 5 with the spacing member 6 mounted thereon is sheathed within the distended unjoined portion 4, the slurry may be contained within the distention, and the liquid portion suitably driven ofi as by the application of heat thereto.

As will be noted, this embodiment in addition to sheathin an electric resistance element within panel ll, simultaneously distends the unjoined portion Within which the resistance element is contained. As will be noted with reference to FIGURE 3, the resistance element may be directly sheathed into tortuously extending tubular passages contained within a solid structure. Such sheathing of the resistance element requires no additional barrier of metal between it and the inner walls of the structure.

FIGURE 6 illustrates another embodiment of this invention employing a different panel 29 fabricated in accordance with the process of the aforesaid patent to Grenell. However, the instant panel difiens over the panel of the preceding embodiment in that the stop-weld material interposed between component sheets is provided in two distinct patterns 3%? and Ell extending sinuously along the length of the panel with the pattern 36 returning by means of a straight portion 32 back to a position adjacent its point of entry. The pattern St) is intended for subsequent sheathing of electrical resistance element 5 with spacing members 6 mounted thereon.

Pattern 30 is returned adjacent its point of entry in order to facilitate subsequent attachment of the ends of resistance elements to a suitable plug for attachment to a source of electrical current. The instant embodiment differs over the previous embodiment in that the resultant unjoined portion within panel 29 defined by the patterns of weld-inhibiting material are distended prior to insertion of the resistance element 5. Also as illustrated,

the unjoined portions 3t} and 31. are distended so that the resultant tubular passages and 34, respectively, are bulged out on only one side of panel 29. Such a one sided distention may be accomplished by conventional methods, for example as illustrated in US. Patent No. 2,866,429.

As with the preceding embodiment, nozzle 35 of a lluid reservoir 36 is inserted at 37 into the inlet of tubular passage 33. Appropriately coiled resistance element 5 having spacing members e mounted thereon, and having an end of the element attached to a leader plug 38 is suitably inserted within reservoir 36, as for example as by being wound on a spool suitably mounted within the reservoir. The reservoir is preferably filled with a slurry of material, such as magnesium oxide which is heat conducting and electrically insulating, and the slurry appropriately pressurized to propel or drive the leader 38 through the tubular passages 33.

Upon being propelled through passages 33, the leader plug 38 with the resistance element secured therethrough sheaths the resistance element within the passages after which the slurry is retained therein and the liquid portion of the slurry driven off.

For this embodiment, the leader plug is illustrated as a hollow cupped structure flaring outwardly from a common point 39 to its open end td, the terminal portion 51 having a configuration corresponding to the distended passage 33. Suitably secured to the forward interior portion of leader plug 3t: by suitable means 42, such as solder or weld, is a stem 43 of any suitable material, such as a strong wire band of metal and the like extending externally out of leader plug 38 with the external end thereof formed into a loop 44 to which an end of the resistance element is appropriately secured.

Where no further distention of tubular passage 33 is desired, leader plug may have its cross-sectional dimension identical with the corresponding portions of tubular passages 33. Where such further distention is not desired, the leader plug 3% is fabricated of yieldable material having a thickness making the open end portions of the leader plug yieldable to the hydraulic pressure employed so that these open end portions will be radially flexible to snugly contact the inner walls of the passageway 33 and form an obturating seal against the hydraulic pressure-s employed.

As indicated above, the leader plug may be employed for further distending the tubular passages 33 upon being propelled therethrough. In such an operation, the portions of the leader plug adjacent the open end d0 may have a cross-sectional corresponding tube but somewhat larger than the internal cross-section of the tubes. With such a leader plug, the terminal portions ll thereof further distend the tubular passages 33 upon passage through them to not only sheath the resistance element therein but in addition to size the passages to the desired cross-sectional configuration.

The element sheathed in the distended panel 29 ad vantageously provides an integral means for defrosting purposes when the panel is employed as an evaporator in refrigerators with the terminal portions of distended passages 34 attached into a circulating refrigerant system. Although the distended passages 33 and 3.4 have been illustrated as parallelly coextending with each other, and in the same stratum within the panel, it is to be understood that the separate distended passages may also be provided in different stratums with each distended passageway system distended out of opposite faces.

Also, although the invention has been described with reference to specific embodiments, materials and details, various modifications and changes, within the scope of this invention, will be apparent to one skilled in the art and are contemplated to be embraced within the invention.

What is claimed is:

1. A heating unit comprising a solid sh'et metal heat conducting structure having continuously integral expanded portions therein defining a multidireetional tubular passage extending thcrethrough, a heat-conducting electric-insulating material filling said passage, a plurality of heat-conducting electric-insulating spacing members embedded in said material at spaced points in said passage from end to end thereof, and an electric heating element sheathed in said passage and extending therein through said material and said members in spaced relat on to the inner wall of said passage, said element being supported by said members.

2. The unit of claim 1 wherein said spacing members are spheres supporting said element in coaxial relation with said wall.

3. A heating unit comprising a plurality of superposed sheets werdcd together, a continuous unwelded band extending between adjacent sheets and welded portions thereof and distended to form a continuously integral expanded portion on at least one surface of said sheets to form a tubular passage therein, said band extending between said adjacent sheets in a maid-directional and unbranched pattern, a heat-conducting electric-insulating material filling said passage, a plurality of heat conducting electric insulating spacing members embedded in said material at spaced points in said passage from end to end thereof, and an electric heating element sheathed in said passage and extending therein through said members and said material, said element being supported by said members in spaced relation to the inner wall of said passage.

4. The unit of claim 3 wherein said spacing members are spheres supporting said element in coaxial relation with said wall.

5. A heating element comprising a solid sheet metal structure containing a multi-direetional tubular passage extending therethrough, said passage being defined by continuously integral portions of the thickness of said sheet expanded to bulge out of at least one of the surfaces of sheet, at least one electric heating element extending through said passage, a plurality of spacer members mounted at spaced points on said element to dispose said element in spaced relation to the inner wall of said passage, and heat-conducting electric-insulating material filling the re; rainder of the volume in said passage.

References (Cited by the Examiner UNITED STATES PATENTS 554,910 2/96 Delany 338-213 1,247,125 ll/l7 Madsen 338-243 1,359,400 1 i/ZO Lightfoot 338243 1,472,197 10/23 Sutherland 338-2l3 2,920,377 l/Gl) lanes.

RICHARD M. WOOD, Primary Examiner, 

1. A HEATING UNIT COMPRISING A SOLID SHEET METAL HEAT CONDUCTING STRUCTURE HAVING CONTINUOUSLY INTEGRAL EXPANDED PORTIONS THEREIN DEFINING A MULTI-DIRECTIONAL TUBULAR PASSAGE EXTENDING THERETHROUGH, A HEAT-CONDUCTING ELECTRIC-INSULATING MATERIAL FILLING SAID PASSAGE, A PLURALITY OF HEAT-CONDUCTING ELECTRIC-INSULATING SPACING MEMBERS EMBEDDED IN SAID MATERIAL AT SPACED POINTS IN SAID PASSAGE FROM END TO END THEREOF, AND AN ELECTRIC HEATING ELEMENT SHEATHED IN SAID PASSAGE AND EXTENDING THEREIN THROUGH SAID MATERIAL AND SAID MEMBERS IN SPACED RELATION TO THE INNER WALL OF SAID PASSAGE, SAID ELEMENT BEING SUPPORTED BY SAID MEMBERS. 